WBSDF for simulating wave effects of light and audio

Abstract

Diffraction is a common phenomenon in nature when dealing with small scale occluders. It can be observed on biological surfaces, such as feathers and butterfly wings, and man-made objects like rainbow holograms. In acoustics, the effect of diffraction is even more significant due to the much longer wavelength of sound waves. In order to simulate effects such as interference and diffraction within a ray-based framework, the phase of light or sound waves needs to be integrated. We introduce a novel method for creating Bidirectional Scattering Distribution Functions (BSDF's) that efficiently simulate diffraction and interference in light and sound in ray-based frameworks. The reflected or scattered radiance of a ray indirectly and independently encodes the mutual phase information among the rays, conveniently allowing for interference after multiple bounces. Previous work has described how to add local diffraction and interference effects to the Bidirectional Reflection Distribution Function (BRDF)[Stam 1999]. However, a traveling ray does not carry phase information and therefore is unable to interfere in a later stage. Our BSDFs, derived from the Wigner Distribution Function (WDF) in wave optics, abstract away the complexity of phase calculations. Traditional ray-based renderers, without modifications, can directly use these WBSDFs.